<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>盒子模型</title>
    <style>
        div {
            width: 300px;
            height: 300px;
            background-color: red;
            padding: 50px;
            border: 3px solid green;
        }
    </style>
</head>
<body>
    <div>
        盒子模型
    </div>
</body>
</html>
